The present invention relates generally to spring suspensions for off-road vehicles such as earth moving machines.
In the past it has been common practice to simply dispense with springing of the chassis in an off-road vehicle such as an earth moving scraper. This has resulted in a rough ride for the operator and the transmission of shocks, often at destructive level, to the vehicle when negotiating rough ground. In those instances where springing has been employed, particularly for off-road vehicles of lighter construction, the tendency has been to utilize the principles of suspension which have been used in automobiles and highway trucks, that is, each wheel has been provided with individual springing and damping means. The individual springing has meant that irregularities in ground contour causing momentary tilting to right or left, must be accommodated by opposite movements in the right and left suspension means. This causes constant and unnecessary exercising of the suspensions on rough terrain with generation of high suspension forces resulting in aggravated wear and high maintenance cost. Moreover, where the wheels are separately sprung with desired softness or compliance there is a sacrifice in roll stability, that is, there is lowered resistance to sway or roll between suspensions at one axle location. As a result, where separate springing is used, it is often necessary to compromise springing, roll stability, or both, in an effort to achieve a practical solution.
Some efforts have been made in the past to depart from individual wheel springing, as evidenced, for example, by an off-road truck of early "Dart" manufacture. In such structure a single horizontal pinned joint was provided between the axle housing and the lower end of the suspension to permit oscillation of the axle housing in a plane transverse to the center line of the vehicle. Such an arrangement, however, subjected the suspension device to rather large side forces and resulted in a coupling of motion in both transverse and longitudinal directions, in addition to the vertical loads required of the suspension. The effects of the side forces and couples were further aggravated by the presence of oscillation limit stops, which required the suspension to support the entire axle load at a wheel at one end of the axle.
In the so-called "cushion hitch" used in certain "Caterpillar" earth moving vehicles, the axle is rigidly attached to the frame or chassis which is connected to the tractor by a joint which permits relative rolling movement about a longitudinal oscillation axis. The only cushioning against bumps and irregularities is that which occurs in the tires, and the only springing is that which is provided between the two main portions of the vehicle i.e., between the front or tractor section and the rest of the vehicle. Moreover, there is no control of "roll stability" about the longitudinal oscillation axis.
More recently an improved suspension has been proposed as covered in copending application Ser. 681,465 filed Apr. 29, 1976 employing a panhard type lever and which, in one arrangement, permits mounting of the main suspension device in an off-center position, leaving the space below the chassis center line clear for installation of other components such as drive elements. It is the purpose of the present arrangement to provide a simplification thereover for use in those instances where complete clearance along the chassis center line is not required.